In antenna systems defining an array of two or more antennas there are differences among the antennas. In particular, propagation pathways differ slightly between antennas, affecting the amplitude and phase of signals being received and transmitted with the antennas. Traditionally, the differences have been accounted for by determining calibration offsets for the antennas. Specifically, a known signal is received and/or transmitted by each of the antennas and the differences in resulting output from the antennas is compared with one another. Based on the differences, calibration offsets are defined to improve performance of the system.
Conventionally, the calibration offsets are determined by an iterative process. The process generally includes receiving and transmitting signals with the antennas, measuring the result, and making adjustments, i.e., modifying calibration offsets. This is repeated until differences in output have been reduced to an acceptable level and nominal best performance achieved. The system is ordinarily tuned by using an accessory or pilot signal. However, best performance is desired for the main signal, not the pilot signal. Therefore, an offset is applied to the pilot signal, and checking for improvement is performed with the main signal. As will be appreciated by those skilled in the art, it is a trial and error procedure, and can be quite time consuming and labor intensive.
Moreover, calibration offsets tend to be heavily dependent upon frequency. For antennas systems required for use over a large frequency range, the foregoing process of trial and error can become costly in terms of the time necessary to complete the process.
In addition, the calibration offsets are typically determined before an antenna system has been installed for use. After the antenna system has been installed, environmental factors can cause differences to change between the antennas, rendering the previously determined calibration offsets to be far from optimal.
An embodiment of a method or process in accordance with the present invention addresses some of the drawbacks of a trial and error procedure. In particular, it provides for a more automated and deterministic procedure that is less time consuming and can be more readily preformed over a wide frequency range. Further, determination of calibration offsets can be performed at least in part after installation of an antenna system.